'\" t
.TH "SD_DEVICE_REF" "3" "" "systemd 255" "sd_device_ref"
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.\" * MAIN CONTENT STARTS HERE *
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.SH "NAME"
sd_device_ref, sd_device_unref, sd_device_unrefp \- Create or destroy references to a device object
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <systemd/sd\-device\&.h>
.fi
.ft
.HP \w'sd_device*\ sd_device_ref('u
.BI "sd_device* sd_device_ref(sd_device\ *" "device" ");"
.HP \w'sd_device*\ sd_device_unref('u
.BI "sd_device* sd_device_unref(sd_device\ *" "device" ");"
.HP \w'void\ sd_device_unrefp('u
.BI "void sd_device_unrefp(sd_device\ **" "device" ");"
.PP
\fBsd_device_ref()\fR
increases the internal reference counter of
\fIdevice\fR
by one\&.
.PP
\fBsd_device_unref()\fR
decreases the internal reference counter of
\fIdevice\fR
by one\&. Once the reference count has dropped to zero,
\fIdevice\fR
is destroyed and cannot be used anymore, so further calls to
\fBsd_device_ref()\fR
or
\fBsd_device_unref()\fR
are illegal\&.
.PP
\fBsd_device_unrefp()\fR
is similar to
\fBsd_device_unref()\fR
but takes a pointer to a pointer to an
\fBsd_device\fR
object\&. This call is useful in conjunction with GCC\*(Aqs and LLVM\*(Aqs
\m[blue]\fBClean\-up Variable Attribute\fR\m[]\&\s-2\u[1]\d\s+2\&. Note that this function is defined as an inline function\&. Use a declaration like the following, in order to allocate a device object that is freed automatically as the code block is left:
.sp
.nf
{
  __attribute__((cleanup(sd_device_unrefp))) sd_device *device = NULL;
  int r;
  \&...
  r = sd_device_new_from_syspath(&device, "\&...");
  if (r < 0) {
    errno = \-r;
    fprintf(stderr, "Failed to allocate device: %m\en");
  }
  \&...
}
.fi
.PP
\fBsd_device_ref()\fR
and
\fBsd_device_unref()\fR
execute no operation if the argument is
\fBNULL\fR\&.
\fBsd_device_unrefp()\fR
will first dereference its argument, which must not be
\fBNULL\fR, and will execute no operation if
\fIthat\fR
is
\fBNULL\fR\&.
.SH "RETURN VALUE"
.PP
\fBsd_device_ref()\fR
always returns the argument, and
\fBsd_device_unref()\fR
always returns
\fBNULL\fR\&.
.SH "HISTORY"
.PP
\fBsd_device_ref()\fR,
\fBsd_device_unref()\fR, and
\fBsd_device_unrefp()\fR
were added in version 251\&.
.SH "NOTES"
.IP " 1." 4
Clean-up Variable Attribute
.RS 4
\%https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
.RE